Uc Davis: Five-year Central Coast study sharpens focus on how harmful bacteria move through produce environments
uc davis is spotlighting initial findings from a major five-year environmental study on California’s Central Coast, aimed at understanding how harmful bacteria can move through the landscape around produce fields. The project was led by the U. S. Food and Drug Administration alongside the Western Center for Food Safety at the University of California, Davis, and it examined environmental pathways that can contribute to food safety risks. The work focuses on a region often called the nation’s “salad bowl, ” which has been linked to several foodborne illness outbreaks, and the findings are being presented as a clearer map of how contamination can persist across time and terrain as of 3/6/2026 (ET).
What the study found first: where harmful E. coli showed up
Researchers testing areas within and surrounding produce fields detected harmful strains of E. coli, including types that can cause serious human illness, in both animal and environmental sources in the region. The study examined soil, surface water, sediment, and air, and also collected feces from livestock and wildlife at numerous ranches and vineyards to better understand how often the bacteria occurs at those locations.
Initial findings show the bacteria appearing in feces from animals including cattle, feral pigs, bobcats, deer, various birds, coyotes, and flies. The study also detected the organisms in older samples at times, which researchers said indicates the bacteria can persist under a range of conditions.
Researchers said the bacteria appeared less often in farm soil overall, but was found more frequently in farm soil near rivers, streams, and cattle ranches. They also detected it in rivers, creeks, and sediment, and less often in irrigation runoff—signaling to the research team that surface water can help bacteria survive and move through the landscape.
How the work was organized—and who was at the table
The FDA asked the Western Center for Food Safety at UC Davis in 2020 to play a central role in the large-scale environmental effort, with the goal of better understanding where disease-causing bacteria come from and how they spread. The study was built on collaboration with the FDA, the California Department of Food and Agriculture, ranchers, landowners, and growers.
“This was a five-year collaborative effort to test the environment within and surrounding produce fields, such as soil, surface water, sediment and air, ” said Rob Atwill, principal investigator for the Western Center for Food Safety and an epidemiologist with the UC Davis Weill School of Veterinary Medicine.
Atwill also underscored the role of producers and livestock partners in the work. “We could not have done this without our partnership with the California livestock and produce industries, ” he said.
Strains, persistence, and what was not detected
Researchers identified multiple strains of E. coli O157: H7 in environmental samples, but they did not detect the strain linked to outbreaks that occurred between 2016 and 2020. Additional strains found in wildlife closely matched those found in cattle, and in some cases matched strains found in water and soil.
Several illness-causing strains were identified, and researchers said some continued to be isolated from the environment for nearly two years.
At one livestock ranch, different E. coli O157: H7 strains were detected each year in both cattle and wildlife, which the researchers said suggests infections were short-lived and that the bacteria may have been circulating among animals. The strain appeared very briefly in two other ranches, and researchers described it as short-lived in those herds as well.
Immediate reactions: what researchers say the results reinforce
Researchers said the findings reinforce a long-standing understanding among scientists and growers: these organisms are naturally present in the environment. Linda J. Harris, co-principal investigator with the Western Center for Food Safety and professor emerita in the UC Davis Food Science and Technology department, said the results confirm much of what had been understood about how bacteria spread.
What’s next
Researchers are framing the work as a detailed environmental look at how contamination can persist and move, particularly where water, wildlife, livestock, and produce production intersect. The next developments to watch will be how the collaborating institutions translate these environmental patterns into practical, field-level actions and continued study focus, as uc davis and partners keep working through the project’s findings and implications for produce-growing regions.
